Framed tension structure

ABSTRACT

A portable, rapidly erected fabric covered building-type structure has a plurality of articulated arch frames which may be hoisted from the ground to extend transversely in longitudinally spaced vertical planes. Spreaders rigidly connect the arch frames. Individual rectangular fabric sections extend transversely between corresponding adjacent pairs of the arch frames to provide an interior sheltered from the outside environment. The side edges of the fabric sections are connected to the rails of removable ladder-like mechanisms carried by the frames for tensioning the sections across their widths. The ends of the fabric sections are also pulled downwardly at the sides of the building by other mechanisms for tensioning the fabric sections lengthwise.

BACKGROUND OF THE INVENTION

The present invention relates to building structures, and moreparticularly, to building structures of the type in which fabric orother web material is stretched over a frame to provide an interiorsheltered from the outside environment.

Fabric covered structures in one form or another have been around forthousands of years. Ancient fabric structures took many forms, from veryprimitive teepees to Arabic palaces. Today, most individuals arefamiliar with circus tents and tents used for camping.

However, the need for relatively inexpensive, portable, rapidly erectedbuilding structures has led to the development of framed tensionstructures able to handle forty pounds of snow per square foot, winds upto one hundred and twenty miles per hour, and having insulation, heatingand cooling comparable to permanent building structures of wood,masonry, concrete or steel.

Framed tension structures which have heretofore been developed havefallen short of obtaining the full potential benefits to be derived fromthis type of construction. Prior designs have been overly complex andexpensive and not well suited to a wide range of sizes.

SUMMARY OF THE INVENTION

It is therefore the primary object of the present invention to providean improved framed tension structure.

It is another object of the present invention to provide an improvedbuilding-type structure of the type in which fabric or other webmaterial is stretched over a load supporting frame.

Another object of the present invention is to provide such a structurein which the frame is covered with a plurality of individual rectangularsections of a flexible web material which are each adjustably tensionedacross their width and length.

It is another object of the present invention to provide a framedtension structure in which individual fabric panels can be quickly andeasily removed with minimum disturbance to the interior of thestructure.

Another object of the present invention is to provide an improved framedtension structure in which the fabric tensioning means operatesindependently of, yet is carried by, a load supporting frame.

Another object of the present invention is to provide an improved framedtension structure which can be assembled on the ground in rapid fashion,and readily erected without cranes or other expensive heavy equipment.

Another object of the present invention is to provide a framed tensionstructure having inner and outer fabric skins to provide better thermalinsulation.

Still another object of the present invention is to provide an improvedframed tension structure which can be readily adapted for constructingstructures in a wide range of sizes.

Still another object of the present invention is to provide an improvedframed tension structure with a minimum amount of hardware andconnectors.

Another object of the present invention is to provide an improved framedtension structure in which fabric or other web material sections arestretched along their planes in two directions by tensioning meanssupported by independent load carrying arch frames.

Still another object of the present invention is to provide an improvedframed tension structure in which individual fabric or other webmaterial panel sections can readily be stretched without scaffolding andby using a simple hand-operated tool.

Yet another object of the present invention is to provide an improvedframed tension structure in which the tensioning mechanisms can be madeof standard, uniform extruded ladder-like mechanisms.

Yet another object of the present invention is to provide an improvedframed tension structure in which the fabric or other web material isstretched by adjustable mechanical means without requiring movement ofthe underlying load supporting frame.

Still another object of the present invention is to provide an improvedframed tension structure in which variable load forces such as thoseimparted by high winds can be readily accommodated by articulating loadsupporting beams.

Yet another object of the present invention is to provide an improvedframed tension structure in which the pitch can be increased to shedsnow in colder environments or decreased in warmer climates to providegreater floor space or less susceptibility to high winds.

Still another object of the present invention is to provide an improvedframed tension structure having novel fabric tensioning means adapted tobe utilized with a wide variety of load supporting frames includingbeams, trusses, and other support configurations.

According to the present invention a portable, rapidly erected fabriccovered building has a plurality of articulated arch frames which may behoisted from the ground to extend transversely in longitudinally spacedvertical planes. Spreaders rigidly connect the arch frames. Individualrectangular fabric sections extend transversely between correspondingadjacent pairs of the arch frames to provide an interior sheltered fromthe outside environment. The side edges of the fabric sections areconnected to the rails of removable ladder-like mechanisms carried bythe frames for tensioning the sections across their widths. The ends ofthe fabric sections are also pulled downwardly at the sides of thebuilding by other mechanisms for tensioning the fabric sectionslengthwise.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a preferred embodiment of my framedtension structure.

FIG. 2 is a simplified side elevation view of two positions of one ofthe articulated arch frames of the preferred embodiment illustrating afirst method of erection.

FIG. 3 is a side elevation view of the preferred embodiment of ourframed tension structure with a portion of its fabric covering cut away.

FIG. 4 is an enlarged side elevation view of a single articulated archframe of the preferred embodiment of our invention with portions brokenaway and illustrating structural details of the same.

FIG. 5 is an enlarged sectional view of the pivoting end of the archframe taken along line 5--5 of FIG. 4.

FIG. 6 is an enlarged sectional view of the rolling end of the archframe pinned in position and taken along line 6--6 of FIG. 4.

FIG. 7 is a greatly enlarged side elevation view taken along line 7--7of FIG. 3 and illustrating the mechanism used to tension a fabricsection in the direction of its length.

FIG. 8 is an elevation view taken from the left-hand side of FIG. 7illustrating the mechanisms of our invention which are utilized totension fabric sections across their widths and along their lengths.

FIG. 9 is an enlarged sectional view taken along line 9--9 of FIG. 8 andillustrating further details of the ladder-like mechanism used totension the fabric sections across their width and also illustrating thefabric flaps which overlap and cover the ladder-like mechanisms.

FIG. 10 is an enlarged view of a portion of the arch frame of FIG. 4illustrating a fixed angular connection of two segments of the frame.

FIG. 11 is an enlarged verical sectional view taken along line 11--11 ofFIG 10 illustrating the I-beam construction of the arch frame.

FIG. 12 is a top plan view of a central hinged joint of one of the archframes of the preferred embodiment illustrating the attached fabricsecuring ladder-like mechanism.

FIG. 13 is a side elevation view of one of the hinged joints of theladder-like structure illustrated in FIG. 12.

FIG. 14 is a greatly enlarged sectional view of one of the side railsand cross rungs of the ladder-like structure taken along line 14--14 ofFIG. 12 and illustrating the manner in which the fabric sections and theflaps are retained in the rail.

FIG. 15 is a side elevation view of a portion of a building constructedin accordance with our invention illustrating a accordion-type endclosure.

FIG. 16 illustrates an alternate, simplified construction of an archframe that may be used in our invention.

FIG. 17 illustrates the manner in which fabric sections of the preferredembodiment of our invention can be tensioned or stretched tight acrosstheir widths by pulling the rails on a ladder-like mechanism closertogether with a winch mechanism so that the rails can be pinned into aposition where the fabric is tight.

FIG. 18 is a simplified side elevation view of two positions of anarticulated arch frame of our invention illustrating an alternate methodof erection utilizing a vertical mast to hoist the center of the frameinto position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 and 3, the preferred embodiment 10 of our framedtension structure includes a plurality of longitudinally spaced archframes 12 which extend transversely in vertical planes. The arch framesare visible in FIG. 3 but are covered by fabric flaps in FIG. 1 whichare hereafter described. Accordingly, dashed lead lines for referencenumber 12 have been utilized in FIG. 1. A pluraliy of spreaders 14 (FIG.3) extend longitudinally between and rigidly connect the arch frames 12.A plurality of rectangular sections 16 (FIGS. 1 and 3) of a flexible webmaterial form the main covering of the structure. Each of these sectionshas a width corresponding to the longitudinal distance between adjacentones of the frames 12 and a length corresponding to the transverseextension of the frames. In other words, each rectangular web section 16extends from ground level on one side of the structure to ground levelon the other side of the structure.

First means hereafter described are mounted on the arch frames 12 foradjustably tensioning each of the rectangular web sections 16 across itswidth between a corresponding adjacent pair of the arch frames. Secondmeans hereafter described are also connected to the frames foradjustably tensioning each of the rectangular web sections 16 in thedirection of its length.

The preferred embodiment of our framed tension structure illustrated inFIGS. 1 and 3 is provided with an end enclosure consisting of two setsof angularly spaced cables 18 which extend downwardly from an end archframe 12. The cables 18 are covered by triangular sections 20 of a webmaterial. A suitable door structure 22 is also provided. The other endof the preferred embodiment of our framed tension structure may becovered by vertically extending web sections (not illustrated) oversuitable vertically extending cables (not illustrated) connected to thearch frame at the other end of the structure.

A wide variety of end enclosures may be utilized with our invention. Forexample, FIG. 15 illustrates a accordion-type end enclosure 24. A secondplurality of arch frames 26 are covered by fabric 28. The arch frames 26are connected at their ends by respective joints 30 mounted to thecorresponding ends of the arch frame 12 at the end of the structure. Thearch frames 26 extend in planes angularly spaced between vertical andhorizontal.

The web material of our preferred embodiment may be any fabric or othermaterial. A wide variety of web materials which have heretofore beenutilized in prior art tensioned frame structures may be utilized.Preferably, the rectangular web sections 16 are made of coated orlaminate polyester vinyl chloride (PVC). By way of example, the laminatePVC may be rated at eighteen ounces per square foot while the coated PVCmay be rated at twenty-two ounces per square foot. A structure using thecoated PVC fabric will not admit as much light as a structure using thelaminate PVC fabric. The difference in weave makes the coated PVC fabricopaque and the laminate PVC fabric translucent. The weave on the coatedPVC fabric is tighter than the weave on the laminate PVC fabric. Thecoating on the coated PVC fabric adheres directly to the weave, whereasthe coating of the laminate PVC fabric adheres to itself as well as tothe weave. Factors to be considered in selecting a web material includeestimated life expectancy, weight in ounces per square foot, tensilestrength, strength of adhesion of the coating, tear strength,hydrostatic strength, blocking (scale rating 1, 2 or 3), cold crease,and flame resistance.

FIG. 4 illustrates the construction of the arch frames 12 of thepreferred embodiment of our frames tension structure. In general, thearch frame 12 is made of a plurality of straight segments 32, 34, 36,38, 40 and 42 of steel I-beam. These I-beam segments are connected endto end and are angularly disposed relative to one another to form anarch. While the arch frames 12 of the preferred embodiment of ourinvention include I-beams, other load support memebers, for exampletrusses, may be utilized. The opposing ends of the I-beams 36 and 38 areconnected for relative articulation by hinge means 44. This hinge meansincludes mating arm plates 46 bolted to opposite central sections of theI-beams 36 and 38 and pivotally connected by a pin 48. The arm plates 46extend far enough past the ends of the I-beam segments to permit thearch frame to articulate between a collapsed position illustrated inphantom lines in FIG. 2 and a raised position illustrated in solid linesin FIG. 2.

The other I-beam segments besides 36 and 38 are connected end to end byrigid angular joint means. Specifically, referring to FIGS. 10 and 11,angular moment plates 50 having a channel-shaped cross section areformed with angularly disposed segments. These moment plate segments areconformably received in opposite sides of the adjacent ends of a pair ofI-beams such as 34 and 36. Preferably one set of ends of the opposingpair of moment plates is secured to one I-beam semi-permanently with nutand bolt combinations. The other ends of the moment plates may then besecured to the adjacent I-beam with removable pin assemblies 52. In thisfashion, when the structure is transported, it may be quickly erectedmerely by attaching the moment plates on one end of an I-beam segment toa corresponding I-beam segment with the removable pin assemblies, thusreducing erection assembly time.

Also visible in FIGS. 10 and 11 are spreader connection brackets 54which are welded to opposite halves of each of the moment plates 50 onthe exposed sides thereof. As illustrated in FIG. 9, the ends of thechannel-shaped spreaders 14 fit over corresponding spreader brackets 54and are secured thereto by releasably pin assemblies 56.

Referring to FIGS. 4 and 5, the ends of the arch frames 12 are connectedto anchors 58 and 58'. A pair of hinge plates 60 (FIG. 5) are attachedto opposite sides of the I-beam segment 32 by bolts 62. The hinge plates60 are bent outwardly at the remote end of the I-beam segment 32.Brackets 54 are welded to each of the hinge plates for connection to thecorresponding spreaders 14.

The anchor 58 (FIG. 5) includes a base plate 64, which may be rigidlysecured to a foundation (not illustrated) such as the ground, concreteslab or some other suitable structure. The anchor 58 further includestrunnions 66 which are welded to the base plate 64 and extend verticallytherefrom at spaced-apart locations. A cylindrical sleeve 68 extendsthrough the remote ends of the hinge plates 60 between the trunnions 66.The ends of the sleeve 68 are threaded and nuts 70 are screwed over thesame to hold the sleeve to the hinge plates. A removable pin 72 extendsthrough the holes in the trunnions 66 and through the center of thesleeve 68 and is held in position by a cotter pin 74.

Referring to FIG. 6, the other end of each of the arch frames 12 hassimilar structure as indicated by the like reference numerals. Inaddition, a ball-bearing wheel 76 is journaled about the sleeve 68between the remote ends of the hinge plates 60.

When the prefered embodiment of our framed-tension structure is erected,each of the arch frames 12 is initially assembled in the generalconfiguration illustrated in phantom lines in FIG. 2. The end of thearch frame having the I-beam segment 32 is pinned to the anchor 58 onthe left side of FIG. 2. The other end of the arch frame is positionedwith its ball-bearing wheel 76 engaged with the foundation outboard ofthe other anchor 58' on the right side of FIG. 2. A cable 78 isconnected to the I-beam segment 42 and is gradually pulled horizontallyacross the foundation by a winch (not illustrated). This causes theball-bearing wheel 76 to roll inwardly along the foundation toward theanchor 58'. This rolling action causes the arch frame to assume theraised configuration illustrated in solid lines in FIG. 2. As the archbeam approaches this raised configuration, the wheel 76 rolls betweenthe trunnions 66 of the anchor 58'. The pin 72 is inserted through theanchor 58' and through the wheel 76. This hold the arch frame in itsraised configuration. The same winch assembly may then be moved to pullnext arch frame into its raised position.

FIG. 18 illustrates an alternate method of erecting each of the archframes 12 of our preferred embodiment. Specifically, a vertical mast 80is used which is illustrated in three different positions in FIG. 18,namely 80a, 80b and 80c. The mast has a pulley 81a rotatably mounted toits upper end. And a cable 81b feeds over the pulley 81a and is used toraise the center of the arch frame. The mast is initially erected in theposition illustrated in phantom lines at 80a in FIG. 18. The lower endof the mast is pivotally mounted to a sliding anchor 82. One end of thecable 81b is attached to the hinge means 44 at the center of the archframe. The end of the arch frame without the wheel 76 is pivotallyconnected to the anchor 58. A winch or other mechanism is then used todraw in the other end of the cable. This causes the arch frame 12 tomove from its collapsed configuration illustrated in phantom lines inFIG. 18 to its raised configuration illustrated in solid lines in FIG.18. The other end of the arch frame having the wheel 76 rolls in alongthe foundation and is secured to the other anchor 58' when the archframe reaches its raised position. At this point, the mast will be inits inclined position illustrated at 80b in FIG. 18. The sliding anchor82 is then moved to the position illustrated at 82' so that the mast isin a vertical position illustrated in phantom lines at 80c in FIG. 18.The mast may then form a part of the structure and help support the roofload. Alternatively, the mast may be removed and used to erect the nextarch frame. As illustrated in FIGS. 3 and 12, a plurality of ladders 84are carried on top of each of the arch frames 12. Each ladder-likemechanism includes a pair of parallel rails 86 (FIGS 8 and 17) and aplurality of rungs 88 which extend perpendicularly between and connectthe rails. As illustrated in FIG. 9, each of the rails extends parallelto and is spaced on either side of the arch frame to which theladder-like mechanism is mounted. The intermediate portion of each ofthe rungs is received in and carried by an upwardly opening channelsection 90 (FIG. 8) welded to the top of the corresponding I-beamsegment of the arch frame. Bolts 92 extend through the sides of each ofthe channel sections and through the nested rung to hold the ladder-likemechanism rigidly in position on the arch frame.

Referring to FIG. 14, each rail 86 is preferably made of extrudedaluminum and has a generally U-shaped cross section. A pair of tubularreceptacles 94 extend along the edges of each rail. Each receptacle hasan outwardly facing slit opening 96 along its entire length.

The side edges of each of the rectangular fabric sections 16 (FIGS. 1and 14) are folded around NYLON rope 98. The overlapping portions of thefabric are stitched or otherwise secured together at 100.

Rectangular flaps 102 (FIG. 9) are provided for covering the openingsthat would otherwise exist between the rails of each of the ladderstructures. As illustrated in FIG. 14, the outer side edge of each flap102 is preferably heat welded or otherwise affixed to the portion of acorresponding fabric section 16 which surrounds the rope 98. Each flaphas a length corresponding to the sum of the lengths of the I-beamsegments making up the arch frames. During assembly of our framedtension structure, the side edges of a fabric section 16 and a flap 102,which are connected, are fed through the upper receptacle 94 of thecorresponding ladder rail 86. The width of each of the flaps 102 issufficient so that the unattached inner side edges of the flaps mountedto the rails of the same ladder may be rolled over into a standing seam104 (FIG. 9). This seam is held together by removable clasps 106 or ropeties (not shown).

Rectangular fabric sections 108 corresponding in length and width to thefabric sections 16 also have their rope surrounding side edges fedthrough the lower receptacle 94 of a corresponding rail 86. The fabricsections 108 thus provide the frame of the building with a second fabriccovering. Each of the fabric sections 16 extends parallel to and isspaced from the plane of the corresponding fabric section 108 lyingimmediately below. The fabric sections 108 may be made of the samematerial as the fabric sections 16. The air space between fabic sectionsimproves the thermal insulation of the building structure.

As illustrated in FIG. 14, the rails 86 of each of the ladder-likemechanisms have holes 110 through which corresponding rungs 88 extend.Each rung is provided with a plurality of longitudinally spaced holes112 (FIG. 8) at each end thereof. The rails of each ladder-likemechanism may be moved toward and away from each other by sliding alongthe rungs 88 which connect the same. Pins 114 (FIG. 17) may be slidthrough holes 116 in the rails 86 and through selected ones of the holes110 in the rungs 88 to fix the spacing between the rails of aladder-like mechanism. The pins 114 may be removably held in position bycotter pins 118 which may be inserted in transversely extending holes inthe forward end of the pins.

Referring to FIG. 17, a winch mechanism 120 may be used to pull therails 86 of a ladder-like mechanism together to stretch the attachedfabric sections 16 across their widths throughout the entire length ofthe ladder-like mechanism. A pair of holes 122 extend through each railon either side of each connected rung 88. The legs of a pair of U-shapedretaining members 124 are inserted in the holes 122 in the rails. Onestrap 126 of the winch mechanism has one end permanently connected tothe intermediate portion of one of the retaining members 124. Anotherstrap 128 has one end permanently connected to the intermediate portionof the other retaining member. The winch mechanism includes a frame madeup of parallel side pieces 130 connected by transversely extending posts132 and 134. The other end of the strap 126 is permanently attached tothe post 132. The other end of the other strap 128 is wound about aspool (not visible). This spool may be rotated about the post 134 bymovement of the lever 136 in the direction indicated by the arrow inFIG. 17. A ratchet mechanism of conventional design is interconnectedbetween the lever 136 and the spool to permit the rails 86 to begradually pulled together by repeated back-and-forth movement of thelever 136 without slippage.

When the preferred embodiment of our framed tension structure iserected, a worker can climb the ladder-like mechanisms and use the winchmechanism 120 as he reaches each rung. Each time the worker inserts theU-shaped retaining members 124 into the rails, inserts a first pin 114to fix the position of one of the rails, then moves the lever 136 topull the other rail toward it. When sufficient tension has been achievedon the fabric section 16 attached to the moving rail, the second pin 114is inserted. The other fabric section 16 is then stretched by removingthe first pin 114, cranking a lever 136 to pull the other rail in therequired distance, and then reinserting the first pin 114. The workerthen removes the U-shaped retaining members 124 and reuses the winchmechanism 120 over the next rung of the ladder-like mechanism. All ofthe ladder-like mechanisms are similarly adjusted to tighten each fabricsection 16 widthwise over its entire length.

As illustrated in FIG. 4, the length of each of the ladder-likemechanisms 84 is equal to the length of the I-beam segment to which itis attached. The adjacent ends of the ladder-like mechanisms are cut ormitered so that when abutted they form the same angle as the underlyingabutting I-beam segments. Where the underlying I-beam segments arerigidly secured together, such as the I-beam segments 34 and 36 (FIG.10), the abutting ends of the ladder-like mechanism carried thereby arerigidly secured together. The abutting rails of the two ladder-likemechanisms carried by the I-beam segments 36 and 38 (FIG. 4) areconnected by hinge means 138 (FIG. 13). This hinge means includeschannel members 140 (FIGS. 12 and 13) secured by bolts 142 to theadjacent rail ends. The members 140 have ears 143 which overlap eachother and are pivotally connected by removable pins 144. These pins 144are held in position by removable cotter pins 146 (FIG. 12). Hinge means44 and 138 pivot together as the arch frame is raised.

Each of the fabric sections 16 is tensioned along its entire length. Asillustrated in FIGS. 7 and 8, the ends of each fabric section 16 nearthe foundation are wrapped around a floating box beam 148 and stitchedor otherwise secured at 150. The ends of the box beam 148 fit over thethreaded legs of hook elements 152. The curved portion of each of thehooked elements are received in holes 154 in the trunnions 66 of theanchors 58 or 58'. Nuts 156 (FIG. 8) are screwed over the threaded legof each of the hook elements 152 and may be tightened to force thefloating box beam 148 downwardly. Thus, when each end of a fabricsection 16 is connected to a floating box beam in this manner,tightening of the nuts 156 will stretch and tension the fabric sectionover its entire length.

The ends of the underlying fabric sections 108 may be wrappped aroundthe same floating box beams as the overlying fabric sections 16. Thus,when the nuts 156 are tightened and a box beam moved downwardly, boththe upper fabric section 16 and the underlying fabric section 108 willbe stretched along its entire length. Alternatively, a secondindependent means for longitudinally stretching the underlying fabricsections 108 may be provided.

Having described preferred embodiments of our framed tension structure,it will be apparent to those skilled in the art that our inventionpermits of modification in both arrangement and detail. For example,articulated arch frames 158 (FIG. 16) may be utilized which have onlyfour angled segments. The longitudinal and lateral fabric tensioningmechanisms of our invention can be incorporated into a wide variety ofother frame structures. Therefore, the protection afforded our inventionshould only be limited in accordance with the scope of the followingclaims.

We claim:
 1. A building structure comprising:a plurality oflongitudinally spaced arch frames extending transversely in generallyvertical planes; a plurality of spreaders extending longitudinallybetween and rigidly connecting the frames; a plurality of rectangularsections of a flexible web material, each web section having a widthcorresponding to the longitudinal distance between adjacent ones of theframes and a length corresponding to the traverse extension of theframes; first means mounted on the frames for adjustably tensioning eachweb section across its width between a corresponding adjacent pair offrames; the first tensioning means includes: a plurality of ladder-likemechanisms each having a pair of parallel rails, a plurality of rungsconnecting the rails; means for adjusting the spacing between the rails;means for attaching the rungs of each ladder-like mechanism to acorresponding frame so that the rails extend transversely; and means oneach rail for retaining a lengthwise edge of a corresponding websection; and second means connected to the frames for adjustablytensioning each web section in the direction of its length.
 2. Abuilding structure according to claim 1 and further comprising aplurality of pairs of rectangular flaps made of a flexible web material,one flap of each pair having one lengthwise edge connected to one railof each pair of rails and the other flap of the pair of flaps having onelengthwise edge connected to the other rail of the pair of rails, theflaps of each pair overlapping each other along the portion thereofadjacent their other lengthwise edges.
 3. A building structurecomprising:a plurality of longitudinally spaced arch frames extendingtransversely in generally vertical planes; a plurality of spreadersextending longitudinally between and rigidly connecting the frames; afirst plurality of rectangular sections of a flexible web material, eachweb section having a width corresponding to the longitudinal distancebetween adjacent ones of the frames and a length corresponding to thetraverse extension of the frames; a second plurality of rectangularsections of a flexible web section having a width corresponding to thelongitudinal distance between adjacent ones of the frames and a lengthcorresponding to the transverse extension of the frames; and adjustablewidth tensioning means mounted on the frames for simultaneouslyadjustably tensioning each first and second web section across its widthbetween a corresponding adjacent pair of frames so that each second websection is parallel to and spaced from the plane of a correspondingfirst web section tensioned between the same frame; said adjustablewidth tensioning means includes: a plurality of ladder-like mechanismseach having a pair of parallel rails; a plurality of rungs connectingthe rails; means for adjusting the spacing between the rails; means forattaching the rungs of each ladder-like mechanism to a correspondingframe so that the rails extend transversely; and means on each rail forretaining the corresponding lengthwise edges of corresponding first andsecond web sections.
 4. A building structure according to claim 3further comprising:adjustable length tensioning means connecting to theframes for simultaneously adjustably tensioning the corresponding firstand second web sections in the direction of their length.